1. Filed of the Invention
The present invention relates to an exposure apparatus and an exposure method for directly exposing an exposure target substrate, and more particularly to an exposure apparatus and an exposure method in which exposure data necessary for direct exposure is sequentially supplied to an exposure engine having a plurality of exposure devices and, based on the thus supplied exposure data, the exposure engine forms an exposure pattern on an exposure target object, for example, an exposure target substrate moving relative to the exposure engine.
2. Description of the Related Art
Generally, a wiring pattern on a wiring substrate is formed by applying a photoresist over the substrate, exposing the photoresist based on wiring pattern design data, and developing and printing the desired pattern on the substrate, followed by etching. In the exposure process, a photomask is usually used.
On the other hand, a patterning method based on direct exposure that does not use any photomasks has been proposed in recent years. According to this method, since corrections for the expansion, shrinkage, distortion, displacement, etc. of the substrate can be made to the exposure pattern in real time or in advance at the exposure data generation stage, remarkable improvements can be achieved in such points as the improvement of the manufacturing accuracy, the improvement of the manufacturing yield, the reduction of the delivery time, and the reduction of the manufacturing cost.
Examples of the patterning method based on direct exposure include a method that forms an exposure pattern by direct exposure by using, for example, a Digital Micromirror Device (DMD), an electron beam exposure machine, or the like. In one prior art example of the patterning method based on direct exposure that uses the DMD, Japanese Unexamined Patent Publication No. 10-112579 discloses a technique in which, when exposing the photoresist formed on an exposure target substrate, pattern data corresponding to the pattern to be exposed is generated and this pattern data is input to the Digital Micromirror Device (DMD), causing each of the micromirrors arranged thereon to tilt according to the pattern data; by thus changing the direction of the light reflected by each micromirror on the DMD as needed, the light is projected onto the resist on the exposure target substrate to form an exposure pattern that matches the pattern data.
FIG. 11 is a diagram schematically showing a conventional direct exposure system. It is to be understood that, throughout the drawings given hereinafter, component elements designated by the same reference numerals are component elements having the same functions.
The direct exposure system 100 comprises an exposure apparatus 101 and a computer 102 connected to the exposure apparatus 101. The computer 102 supplies exposure data to the exposure apparatus 101 and controls the exposure apparatus 101. The exposure apparatus 101 comprises a stage 110 on which an exposure target substrate 151 is mounted, and an exposing means 111 which moves in relative fashion over the surface of the exposure target substrate 151 in a direction indicated by an arrow in the figure. The exposing means 111 is equipped with one or more exposure engines (not shown) which are each assigned an area to be exposed on the surface of the exposure target substrate 151 and perform exposure operations in parallel. In each exposure engine, a plurality of exposure devices (not shown) for modulating light sources are arranged in a two-dimensional array. For example, when the direct exposure system 100 is of the type that uses the DMD, the micromirrors of the DMD correspond to the exposure devices.
FIG. 12 is a diagram showing the operating principle of the conventional exposure apparatus.
The exposing means 111, which moves in a relative fashion over the surface of the exposure target substrate 151, is equipped with a plurality of exposure engines #1 to #N (reference numeral 30) (N is a natural number) arranged in a direction perpendicular to the direction of the relative movement of the exposure target substrate 151. While the exposure target substrate 151 is moving relative to the exposure engines #1 to #N (reference numeral 30) at speed Vex, a stage controller 29 generates a signal synchronized to the relative movement (hereinafter called the “synchronizing signal”) and supplies it to each of the exposure engines #1 to #N (reference numeral 30).
The exposure target substrate 151 is divided in a virtual manner into N areas called the “strips #1 to #N” (reference numeral 32). The exposure engines #1 to #N (reference numeral 30), while moving relative to the exposure target substrate 151 at speed Vex, perform exposure on their respectively corresponding strips #1 to #N (reference numeral 32). Here, the length of the exposure target substrate 151 in the direction of the relative movement (hereinafter referred to as the “length of the exposure target substrate), that is, the length of each of the strips #1 to #N (reference numeral 32), is denoted by LY (hereinafter referred to as the “strip length”). Likewise, the length of the exposure target substrate 151 in the direction perpendicular to the direction of the relative movement (hereinafter referred to as the “width of the exposure target substrate) is denoted by LX.
The area that each of the exposure engines #1 to #N (reference numeral 30) can expose at a time is limited. The width of the area on the exposure target substrate 151 that each exposure engine can expose in the direction perpendicular to the direction of the relative movement is not larger than the width ΔX of each of the strips #1 to #N (reference numeral 32) (hereinafter referred to as the “strip width”). Here, the relation LX=N×ΔX holds.
On the other hand, the length of the area on the exposure target substrate 151 that each exposure engine can expose in the direction of the relative movement is shorter than the strip length LY. Accordingly, each of the strips #1 to #N (reference numeral 32) is subdivided in a virtual manner into M “exposure blocks (i, j) (here, M is a natural number, while 1≦i≦N and 1≦i≦M)” (reference numeral 33), and the exposure engine exposes these exposure blocks (i, j) in sequence. When the length of each exposure block (i, j) in the direction of the relative movement is denoted by ΔY, the relation LY=M×ΔY holds between the strip length LY and the length ΔY of each exposure block (i, j) in the direction of the relative movement.
The exposure data is typically data based on bitmap data. Since bitmap data contains a huge data amount, generating and storing the bitmap data prior to exposure would not be preferable as it would consume large memory resources. Therefore, to conserve the memory resources, for each of the exposure engines #1 to #N (reference numeral 30) the exposure data in bitmap form is generated based on design data in real time during the exposure process by dividing the data in a virtual manner for each of the exposure engines #1 to #N (reference numeral 30), that is, for each of the strips #1 to #N (reference numeral 32), and for each exposure block (i, j) in each of the strips #1 to #N (reference numeral 32); the thus generated data is first temporarily stored in memory, and then sequentially supplied to each corresponding one of the exposure engines #1 to #N (reference numeral 30). Accordingly, each of the exposure engines #1 to #N (reference numeral 30) performs the direct exposure based on the exposure data of bitmap form supplied for each exposure block (i, j). The series of these operations is performed based on the synchronizing signal that the stage controller 29 supplies as the reference signal to each of the exposure engines #1 to #N (reference numeral 30).
FIG. 13 is a flowchart showing the data processing flow in the conventional direct exposure apparatus.
As shown in FIG. 13, first the design data 51 is converted into intermediate data 52 in a first data conversion process S101. As the size of the intermediate data 52 is small compared to the size of the bitmap data, and as the first data conversion step S101 need not be performed in real time during the exposure process, the intermediate data 52 may be generated in advance and stored in memory.
In step S102, the intermediate data for one exposure block is read. Next, an alignment/correction step S103 is performed on the intermediate data thus read for one exposure block, and bitmap data 53 is generated in step S104 and temporarily stored in memory. In step S105, the generated bitmap data 53 is supplied to the corresponding exposure engine in synchronism with the synchronizing signal. Here, the realtime process performed in the above steps S102 to S105 is collectively referred to as the “second data conversion process.” Using the bitmap data 53 supplied for each exposure block through the second data conversion process, the exposure engine performs the direct exposure in step S106. When the exposure on the one exposure block by the exposure engine is completed, the process returns to step S102, where the second data conversion process is performed to obtain the bitmap data 53 for the next exposure block. To describe the above series of processing in another way, in step S106 the exposure engine is “consuming”, at a constant speed, the bitmap data 53 “produced” through the second data conversion process in synchronism with the synchronizing signal generated by the stage controller 29.
FIG. 14 is a schematic diagram illustrating the concept of the exposure data of bitmap form used in the direct exposure process by the conventional direct exposure apparatus.
The exposure data is data based on bitmap data composed of pixels arranged in a matrix of n rows and m columns (n and m are integers) as shown schematically in FIG. 14. The coordinates of each pixel in the bitmap data are represented by g(r, c). Here, r indicates the row number in the bitmap data (0≦r≦n−1, where r is an integer), and c indicates the column number in the bitmap data (0≦c≦m−1, where c is an integer). The resolution, i.e., pixel spacing (hereinafter called the “unit pixel spacing”), of the bitmap data is denoted by b. It can be said that the schematic diagram of the bitmap data illustrated in FIG. 14 directly represents the exposure pattern formed (or to be formed) on the surface of the exposure target substrate mounted on the stage (not shown).
FIG. 15 is a schematic diagram illustrating the arrangement of light sources in one exposure engine that performs the direct exposure using the exposure data shown in FIG. 14. Open circles in the figure indicate the light sources.
The exposure engine that uses bitmap data such as shown in FIG. 14 usually has light sources arranged in a two-dimensional array as shown in FIG. 15. The light sources are arranged in a corresponding relationship to the bitmap data of FIG. 14; that is, m light sources per row are arranged in the column direction, and the spacing of the light sources is equal to b which is the same as the resolution (i.e., the unit pixel spacing) of the bitmap data. The column number c of the bitmap data directly corresponds to the column number c of the light source in the exposure head.
As for the light source arrangement in the row direction, the exposure head is designed so that the spacing D between the rows is equal to p times (p is an integer) the unit pixel spacing b in the bitmap data, that is, D=pb. Here, k light sources per column are arranged in the row direction, and the row number is represented by R (0≦R≦k−1, where R is an integer).
The light sources can be switched on and off independently of each other a predetermined maximum number of times per unit time (called the “frame”). This switching speed is called the frame rate f. For example, when the exposure apparatus is of the type that uses the DMD, the angular switching rate of each micromirror (i.e., the modulation rate of the DMD) corresponds to the frame rate f, and the angle of each micromirror is controlled for each frame.
The exposure target substrate mounted on the stage (not shown) moves relative to the exposure engine (i.e., the light sources) at a constant speed in a prescribed direction. That is, the bitmap data shown in FIG. 14 also moves in a virtual manner relative to the exposure engine (i.e., the light sources) shown in FIG. 15. This virtual relative movement of the bitmap data is accomplished by sequentially supplying the necessary bitmap data to the exposure engine in synchronism with the synchronizing signal that the stage controller supplies as the reference signal.
FIGS. 16A, 16B, 17A, and 17B are schematic diagrams for explaining the relationship between the bitmap data shown in FIG. 14 and the light source arrangement in the exposure engine shown in FIG. 15. As stated previously, the bitmap data schematically shown in the figure corresponds to the exposure pattern formed (or to be formed) on the surface of the exposure target substrate mounted on the stage (not shown). Here, the case where the exposure target substrate moves at speed Vex relative to the light sources R in a virtual manner in a direction indicated by an arrow in the figure, is considered. In the figure, to simplify the illustration, only some of the light sources in the third column are shown, and the other light sources are not shown.
First, as the initial condition, consider the case where the light source R=0 is aligned with the pixel g(0, 3) in the bitmap data, as shown in FIG. 16A. In this condition, the synchronizing signal is sent to the exposure engine, causing the light source R=0 to emit light and thus exposing the pixel g(0, 3).
When, from the initial condition, the exposure target substrate mounted on the stage moves relative to the light source by a distance corresponding to the resolution (i.e., the unit pixel spacing) b of the bitmap data (FIG. 16B), the synchronizing signal is again sent to the exposure engine. At this time, the pixel g(1, 3) comes into alignment with the light source R=0, and the pixel can thus be exposed. As the light source spacing D (=pb, where p is an integer) is sufficiently larger than the resolution b of the bitmap, the pixel g(0, 3) in FIG. 16B is not aligned with any light source, and is therefore not exposed.
When the exposure target substrate mounted on the stage further moves relative to the light source by the distance b (FIG. 17A), the synchronizing signal is again sent to the exposure engine. At this time, the pixel g(2, 3) comes into alignment with the light source R=0, and the pixel can thus be exposed. On the other hand, at this time, the pixels g(0, 3) and g(1, 3) are not aligned with any light source, and are therefore not exposed.
When the exposure target substrate mounted on the stage further moves relative to the light source by the distance b (FIG. 17B), the synchronizing signal is again sent to the exposure engine. At this time, the pixel g(3, 3) comes into alignment with the light source R=0, while the pixel g(0, 3) comes into alignment with the light source R=1; as a result, these pixels can be exposed. On the other hand, at this time, the pixels g(1, 3) and g(2, 3) are not aligned with any light source, and are therefore not exposed.
Thereafter, each time the exposure target substrate mounted on the stage moves relative to the light source by the distance b, the synchronizing signal is sent to the exposure engine, and any pixel that comes into alignment with the light source can be exposed. For example, in the case of the pixel g(0, 3), when the exposure target substrate mounted on the stage moves in a relative fashion by the distance pb from the initial condition, the pixel comes into alignment with the light source R=1, and the pixel can thus be exposed a second time. In the case of the pixel g(1, 3), for example, when the exposure target substrate mounted on the stage moves in relative fashion by the distance (p+1)b from the initial condition, the pixel comes into alignment with the light source R=1, and the pixel can thus be exposed a second time.
In this way, as the exposure target substrate moves in relative fashion below the exposure engine having k light sources in each column, each spot on the exposure target substrate which corresponds to each pixel in the bitmap data can be exposed to light a total of k times. In the direct exposure apparatus, whether the intended exposure process is completed or not is determined by whether the light energy accumulated through k exposures exceeds the threshold for exposing the photoresist applied on the exposure target substrate. Accordingly, if the number, k, of light sources is sufficiently large, then even if some of the k light sources fail to emit light properly due to the failure of micromirrors in the DMD or of driving transistors in the LCD, the possibility that such failure will have a serious effect on the final exposure result is small. Stated another way, such redundancy in the number of light sources constitutes the basis of the reliability of the direct exposure apparatus.
As described above, since the amount of the exposure data is very large, the exposure data is generated based on design data in real time for each exposure block during the exposure process in order to conserve memory resources, and the generated exposure data is supplied to the corresponding exposure engine. That is, the exposure data “produced” for each exposure block in real time in the second data conversion process in FIG. 13 is sequentially “consumed” for each exposure block at a constant speed by the corresponding exposure engine.
The amount of the bitmap data composed of pixels arranged in n rows and m columns (n and m are integers) that the exposure engine of frame rate f “consumes” per unit time is proportional to “m×n×f”, i.e., the product of m, n, and f. The product “m×n×f” is generally known as the “bandwidth”, which is expressed in “bits/sec”. The bandwidth is a measure of the capacity of data transmission between the exposure engine and the memory device in which the bitmap data is stored, and usually there is an upper limit value dependent on system configuration, etc.
It will be easily understood that the width ΔX of the strip on the exposure target substrate 151 that each exposure engine can expose is proportional to the number, m, of columns in the bitmap data when one considers that the bitmap data of n rows and m columns is supplied to the exposure engine. Accordingly, for an exposure target substrate having a certain width LX (=N×ΔX), the larger the number, m, of columns in the bitmap data, the smaller the number of exposure engines required to cover the width LX of the exposure target substrate, and thus the cost of the exposure engines can be reduced correspondingly. That is, by using exposure devices having a larger number of pixels for the exposure engines, the number, m, of columns in the bitmap data can be increased. For example, when the direct exposure system is of the type that uses the DMD, the number of pixels increases in the order of SVGA, XGA, and SXGA.
At this time, when there is an upper limit to the bandwidth, that is, when the bandwidth imposes a constraint on the system configuration, if the number, m, of columns in the bitmap data is increased, the value of the product “m×n×f” naturally increases and, as a result, the frame rate f has to be reduced. Reducing the frame rate f means reducing the exposure speed of the direct exposure system, that is, reducing the throughput of the direct exposure process, which is not desirable. To address this, a method for increasing the exposure process performance of the direct exposure system without reducing the frame rate f is disclosed in Japanese Patent Publication NO. 2004-1244; according to the technique described therein, of the exposure devices arranged in a two-dimensional array in the exposure engine, a smaller number of exposure devices than the total number are used for direct exposure.
Here, if there is no upper limit value on the bandwidth, as the amount of data proportional to the product “m×n×f” has to be processed, there can occur cases where the processing performance of CPU or FPGA that performs the data processing becomes a bottleneck.
As described above, the larger the number, m, of columns in the bitmap data, the smaller the number of exposure engines required to cover the width LX of the exposure target substrate, and thus the cost of the exposure engines can be reduced correspondingly; further, the higher the frame rate f, the faster the exposure speed of the direct exposure system can be made, which therefore can be said to be desirable. In reality, however, an upper limit value dependent on system configuration exists on the bandwidth that defines the capacity of data transmission between the exposure engine and the memory device in which the bitmap data is stored. With the technique disclosed in the above-cited Japanese Patent Publication NO. 2004-1244, as, of the exposure devices arranged in a two-dimensional array in the exposure engine, a smaller number of exposure devices than the total number are used for direct exposure by reducing the number, n, of rows in the bitmap data, a certain degree of effect can be achieved even when there is an upper limit to the bandwidth. However, not all the exposure devices, but selected ones of the exposure devices in the exposure engine, are actually used for direct exposure, and the remaining exposure devices are not used. That is, as all the exposure devices in the exposure engine are not used effectively, the efficiency is low.
In view of the above problem, it is an object of the present invention is to provide an exposure apparatus and an exposure method that can perform high-speed and efficient direct exposure based on exposure data sequentially supplied to each exposure engine having a plurality of exposure devices.